A liquid crystal display device with a COG mounting structure has a structure in which an IC chip, which functions as a driver, is directly mounted to a substrate surface located at a peripheral section of the liquid crystal display device. IC chip mounting techniques are broadly divided into face-down bonding techniques and face-up bonding techniques. The former enables a mounting area to be made smaller than that of the latter, and in addition, the wiring for mounting in the former technique is shorter than in the latter technique, making a face-down bonding technique suitable for use in a display device for which high-speed communications, excellent noise characteristics, compact size, a thin profile, and increased speed are demanded.
An IC chip mounted using a face-down bonding technique is mounted by placing the surface side having a connection surface so as to face downward and bonding by thermocompression. Therefore, a projection connection terminal called a bump is disposed on the bottom surface side of the IC chip. Specifically, the IC chip is formed into a rectangular shape in plan view, for example, and an input bump group in which a plurality of input bumps is aggregated on the bottom surface of one of the longer sides, and an output bump group in which a plurality of output bumps is aggregated on the bottom surface of the other of the longer side are respectively arranged on the IC chip.
As a method of mounting an IC chip in this manner onto the surface of a liquid crystal display panel substrate, it is preferable that an anisotropic conductive film (ACF) connection technique by which the IC chip is connected to the substrate surface via an ACF containing a large number of conductive particles in an adhesive having insulating properties be used because this technique enables the realization of high-density mounting. In the ACF connection technique, a bump on the IC chip and a connection terminal disposed at a location on the liquid crystal panel where the IC chip is to be mounted are electrically connected by interposing the conductive particles inside the ACF therebetween and compressing these particles flat.
To reliably establish a conduction state between an IC chip bump and a connection terminal of the liquid crystal display panel, when bonding the IC chip by pressure, it is preferable that the pressure applied to the conductive particles interposed between the IC chip bump and the liquid crystal display panel connection terminal be uniform for all sets of corresponding bumps and connection terminals, and that the flatness state of the conductive particles be made uniform at all bump connection locations; but in reality, this is not the case.
That is, it is normal for the total areas of the connection surfaces formed by end surfaces of the bumps in the input bump group and output bump group to differ, and therefore the amount of conductive particles trapped between the input bump group and the output bump group, and the connection terminals of the liquid crystal display panel at IC chip pressure bonding time differs in proportion to the difference in the total areas. As a result of this, the pressure applied to the trapped conductive particles at the input bump connection locations and the output bump connection locations changes, and the flatness state of the conductive particles ceases to be uniform at these input bump and output bump connection locations.
When this happens, the conductive particles, for which the pressure applied at IC chip pressure bonding time is relatively low, have a lower degree of deformation and do not become particularly flat, thereby making it impossible to ensure an adequate connection area between a bump and a connection terminal having the conductive particles interposed therebetween, and raising the likelihood of electrical connection defects occurring. However, when the pressing force applied to the IC chip at pressure bonding time is too strong, an excessive load is placed on the conductive particles, causing the particles to undergo compositional deformation, which makes it impossible to obtain a good conduction state between the bump and the connection terminal having the conductive particles interposed therebetween.
Accordingly, configurations for making the flatness state of the conductive particles at all bump connection locations as uniform as possible have been proposed for some time. Patent Document 1 discloses a configuration in which the relationship between the total area S of the connection surfaces (mounting surfaces) of the input bumps, the total area T1 of the connection surfaces of a row of output bumps located on the inner side of the chip, and the total area T2 of the connection surfaces of a row of output bumps located on the outer side of the chip was set to S≧T1>T2 and S≧T1+T2 in an IC chip in which a plurality of output bump arrangements was disposed in a so-called zigzag configuration, for example.